What a find! Stone-age tools in a Boulder backyard.

Douglas Bamforth holds up one of 83 stone artifacts buried in the backyad of Patrick Mahaffy (right). Some of the implements had protein residue belonging to Pleistocene camels, horses, sheep, and bear.

Mr. Mahaffy is president and CEO of a pharmaceutical company based in Boulder. His contractor was digging up the backyard when he lifted a shovelful of dirt out of an 18-inch-deep hole he'd dug. It revealed a cache of what looked like stone tools.

No one had a clue how old they were until Mahaffy rang University of Colorado anthropologist Douglas Bamforth. Analysis of the soil layer and of the shapes of the 83 tools the cache contained pointed to the Clovis culture. The term refers to people who migrated to North America from Asia about 13,000 years ago. The culture is thought to have thrived for about 500 years.

The find is remarkable not only for the number of Clovis implements in one spot, but also because it's one of the few such caches in North America. Based on studies of the surrounding soil, the cache appears to be at the edge of an old flow route for water draining from the nearby Flatiron Mountains, on the outskirts of Boulder.

Are these for real?

Fakes? During a phone chat, Dr. Bamforth says he and a colleague, Peter Birkeland considered the possibility. But the hunt for blood on the tools turned up four blades, each with a different type of blood residue – each belonging to a different animal. The rock tools are slightly weathered, and they also bear the scrapes and scuffs one would expect if they had been bouncing around in someone's pouch or bag for a while.

And the striped tool in the foreground of the photo? It might look like a wooden fake, but it's not, Bamforth explains. It's a layered stone typical of northwestern Colorado and southern Wyoming, which at one time was an ancient sea floor.

So tell us about those folks

Now comes the fun part – trying to piece together the story of the person or persons who stowed the tools.

"It's clear they were deciding what to store," Bamforth says. So was this a favorite hunting ground? Maybe a place to spend spring and summer? After all, the stones themselves came from northwestern Colorado. "We don't know if this was one curmudgeon wanting to get away or a whole group of people," he says.

What is clear is that each known cache of tools is slightly different, he explains. Some only have spear tips. Others have knives and spear tips. This one has large and small knives, what looks like a double-blade ax head, and stone scraps, as though the owner or owners were perhaps anticipating a need to make more tools.

Lots of fodder for speculation. Some of the answers may come through additional, more detailed analysis.

In the meantime, Bamforth is enjoying the moment. The cache is a rich find. "I'll never have this happen again," he says.